Repositorio Institucional de Documentos

1 2 INDEX 1. Abstract...................................................................................................................... 6 2. Resumen .................................................................................................................... 8 3. -Introduction ............................................................................................................ 11 3.1. -Definition of sludge ........................................................................................ 11 3.2. -Different process to get sludge ....................................................................... 11 3.3. -Sewage sludge characterization ...................................................................... 12 3.4. -Uses of sludge................................................................................................. 15 3.5. -Phosphorous in the soil and in sludge ............................................................ 17 3.6. -Heavy metal concentration in sludge, and its effects in the soil..................... 22 3.7. -Effect of sludge on the plant and the soil ....................................................... 25 4. Research objectives ................................................................................................. 37 5. -Material and methods ............................................................................................. 39 5.1. -Measurements ................................................................................................. 42 5.1.1. -Dry matter (%)......................................................................................... 42 5.1.2. -pH and electrical conductivity (EC) ........................................................ 43 5.1.3. -Phosphorous fractions ............................................................................. 44 5.1.4. -Elemental analysis using ICP-OES ......................................................... 46 5.1.5. -Nitrogen and carbon content and ratio .................................................... 51 5.1.6. -Statistical analysis ................................................................................... 51 5.2. -Evaluation of sludge of agricultural use ......................................................... 51 5.2.1. -Legal requirements .................................................................................. 51 5.2.2. -Fertilization dosage ................................................................................. 52 5.2.3. -Final nutrient balance .............................................................................. 53 6. -Results .................................................................................................................... 54 3 6.1. -Chemical characterization of the soil ............................................................. 54 6.2. -Chemical characterization of sludge and manure. .......................................... 56 6.3. -Nutrient extraction by each crop..................................................................... 83 6.4. -Legal requirements ......................................................................................... 84 6.4.1. -Soil characteristics................................................................................... 84 6.4.2. Legal heavy metal concentration in sludge and manure........................... 85 6.4.3. -Maximum heavy metal load in the soil ................................................... 90 6.5. -Fertilization dosage......................................................................................... 97 6.5.1. -Fertilization dosage according to Nitrogen extractions........................... 97 6.5.2. -Fertilization dosage according to Phosphorus extractions ...................... 99 6.5.3. -Fertilization dosage according to Potassium extractions ...................... 101 6.6. -Nutrient balance after fertilization and cropping.......................................... 103 6.6.1. -Nutrient balance after Nitrogen based fertilization and cropping ......... 103 6.6.2. -Nutrient balance after Phosphorus based fertilization and cropping..... 104 6.6.3. -Nutrient balance after Potassium based fertilization and cropping ....... 105 7. -Discussion ............................................................................................................ 107 7.1. -Chemical characterization ............................................................................ 107 7.1.1. -Phosphorus fractions ............................................................................. 107 7.1.2. -Nitrogen and Carbon content ................................................................ 108 7.1.3. -Electrical conductivity and pH .............................................................. 109 7.1.4. -Potassium content .................................................................................. 110 7.1.5. -Manganese content ................................................................................ 111 7.1.6. -Sodium content ...................................................................................... 112 7.1.7. -Copper content ...................................................................................... 112 7.1.8. -Chromium content ................................................................................. 113 7.1.9. -Zinc content ........................................................................................... 113 7.1.10. -Lead content....................................................................................... 114 4 7.1.11. -Sulfur content..................................................................................... 115 7.1.12. -Silicon content ................................................................................... 115 7.1.13. -Aluminum content ............................................................................. 115 7.1.14. -Iron content ........................................................................................ 116 7.1.15. -Arsenic content .................................................................................. 116 7.1.16. -Cadmium content............................................................................... 117 7.1.17. -Calcium content ................................................................................. 117 7.1.18. -Magnesium content............................................................................ 118 7.1.19. -Nickel content .................................................................................... 118 7.2. -Legal requirements ....................................................................................... 119 7.3. -Fertilization dosage....................................................................................... 120 7.3.1. -Nitrogen based dosage........................................................................... 120 7.3.2. -Phosphorus based dossage..................................................................... 122 7.3.3. -Potassium based dosage ........................................................................ 123 7.3.4. Final fertilization election ....................................................................... 123 8. -Conclusions .......................................................................................................... 126 9. Acknowledgments ................................................................................................. 128 10. -References ........................................................................................................ 130 5 6 1. Abstract Sludge.production is increasing worldwide, and one of the main uses of sludge is the use on agricultural land as fertilizer, if they fulfil the legal requirements that limits the use of sludge in agriculture according to its heavy metal content. This study evaluates the main chemical parameters. (Phophorus fraction, Nitrogen, Carbon, CN ratio, pH, Electrical Conductivity, Aluminium, Arsenic, Calcium, Cadmium, Chromium, Copper, Iron, Potassium, Magnesium, Manganese, Sodium, Nickel, Lead, Sulphur, Silicon and Zinc) that allows to know its possible use in agriculture and its dosage. This study is done using sewage sludge samples from 5 different places in Finland and two different manure samples from cow farms in Finland, taking 6 samples per each place and analysing the previously mentioned parameters following the official analysis methods. After that it was carried out an statistical analysis of the data, and using this data a dosage is made according to the legal requirements and the agronomic properties (macronutrient content, NPK). According to the obtained results all sludge samples fulfils the legal requirements to be used in agriculture established in European, Spanish and Finnish legislation . The result show significant differences between chemical characterizations of both products. Regarding sewage sludge samples, the highest differences between each samples are found in phosphorus fractions, that’s varies from place to place, there are also differences in nitrogen content, electrical conductivity, pH, aluminium, calcium, chromium, magnesium, manganese, sodium, iron and sulphur content . In manure the differences between each sample are also found in phosphorus fractionation, pH, nitrogen content, CN ratio, copper, sodium, magnesium and potassium. Copper content is the most limiting factor for agricultural application, due to the limitation established by legislation. Using the maximum amount of sludge that can be legally used according to its copper content, there is enough phosphorus to compensate phosphorus crop requirements, in the other hand there is nitrogen and potassium deficit. Manure is not affected by legislation but its high nickel content could have negative effects in the plant and the soil. 7 The recommended application rate (for a rotation of maize, oilseed rape, hemp and fallow) for those sludge are between 16.000 and 24.000 kg ha-1 of sludge (depending on the copper content and humidity of the sludge sample) every cycle of four years. There would be needed an extra application of mineral fertilizer one year after sludge application and two year after sludge application in the order of 200-250 kg ha-1 of nitrogen and 100 kg ha-1 of potassium. 8 2. Resumen La producción de lodos está aumentando en todo el mundo, y uno de los principales usos que se les puede dar es la aplicación agrícola como fertilizante, siempre y cuando se ajusten a las limitaciones que legales sobre todo en cuanto a presencia de metales pesados. En este estudio se evalúan las principales características químicas (Fracciones de fósforo, Nitrógeno, Carbono, CN ratio, pH, Conductividad Eléctrica, Aluminio, Arsénico, Calcio, Cadmio, Cromo, Cobre, Hierro, Potasio, Magnesio, Manganeso, Sodio, Nickel, Plomo, Azufre, Silicio and Zinc) que permiten conocer su posible utilización en agricultura y la dosificación de estos materiales. Se trabaja con lodos de 5 depuradoras de Finlandia y estiércol procedente de dos granjas de vacuno también en Finlandia; se toman 6 muestras de cada material y se analizan los parámetros indicados anteriormente siguiendo métodos oficiales de análisis. Se realiza un análisis estadístico de los datos obtenidos y se ajusta la dosificación de los lodos teniendo en cuenta: en primer lugar la limitación legal por metales pesados y en segundo lugar el valor agronómico de dichos lodos según su aporte en macronutrientes (N, P y K). Con los datos obtenidos en los análisis, ninguna muestra de lodos supera los valores legalmente establecidos para todos los metales pesados, tanto en la directiva comunitaria como en las regulaciones nacionales en Finlandia y España. Los resultados muestras diferencias significativas entre las características químicas de lodos y estiércol. Dentro de las muestras de lodo, se encontraron diferencias entre las muestras en las fracciones de fósforo, contenido en nitrógeno, conductividad eléctrica, pH, aluminio, calcio, cromo, magnesio, manganeso, sodio, hierro azufre. En los estiércoles se encontraron diferencias entre ambas muestras en las fracciones fósforo, pH, contenido en nitrógeno, CN ratio, cobre, sodio, magnesio y potasio. El cobre ha sido el elemento que ha limitado la máxima cantidad de lodo que se puede aplicar legalmente en el suelo de acuerdo a la actual legislación vigente. Esta dosis casi cubre totalmente las necesidades de fósforo por los cultivos, pero no así las de nitrógeno y potasio. El estiércol no está incluido en esta legislación, pero su contenido en niquel podría tener efectos negativos en planta y suelo. La dosis recomendada (para una rotación de maíz, colza, cáñamo y barbecho) para los lodos analizados son entre 16.000 y 24.000 kg ha-1 (dependiendo del contenido en cobre 15 3.4. -Uses of sludge The sewage sludge production has been increased gradually worldwide. The total production of sludge as dry matter in European Union in 1992 was 5.5 Mt, and in 2005 was about 9 Mt (Eshtiaghi et al., 2013). The production of the sludge is still increasing yearly (Figure 1) due to the fact that the legislation of European Union as well as of many other countries is making compulsory to have water treatment plants in agglomeration of more than 2000 people (91/271/EEC). Also, it is due to the increase of the European population (Eshtiaghi et al., 2013). Sludge can be utilized in various ways (i.e. incineration, landfilling, land application as a fertilizer and as construction material). It can be also utilized in forestry proposes, however it is not common. In some countries, it is forbidden to use sewage sludge on cropland (European commission, 2000c; Przewrocki et al., 2004; Fytili and Zabaniotou, 2008). The use of sludge on cropland is increasing yearly (Lundin et al., 2004; Fytili and Zabaniotou, 2008). The sludge is used as a fertilizer on cropland because of the high nutrient content and organic matter in such sludge which can improve the physical and chemical properties of the soil (Przewrocki et al., 2004; Fytili and Zabaniotou, 2008). However, there are some disadvantages of applying sludge on cropland such as the high content of heavy metals and some pollutants which can be potential problem for the environment (Fytili and Zabaniotou, 2008). In addition, there is a concern about the presence of pathogens that can cause some diseases for the animals and humans (European Commission, 2000b; Przewrocki et al., 2004; Fytili and Zabaniotou, 2008). Incineration is the process where the sludge is combusted for energy production. It is necessary at beginning to reduce the water content of the sludge to reduce the energy consumed (Fytili and Zabaniotou, 2008; Ludin et al., 2004; Przewrocki et al., 2004). Nevertheless, during the combustion process, there is a generation of greenhouse gases (GHG) such as NOx and SOx, in addition to some toxic compounds such as heavy metals and volatile organic compounds. However, such these materials can be reduced by the treatment of flue gas (Rulkens, 2007). Finally, the incineration of sludge is a noisy, dusty and odorous process which can cause some problems for the human where they live (European commission, 2000d; Ludin et al., 2004). 16 Landfilling is the process where the sludge is burial in a specific place for waste residues (Przewrocki et al., 2004; Fytili and Zabaniotou, 2008). If there is no good management for this process in the proper way, some problems with the leachates and gas emissions can occurs which most of them can result in greenhouse effect (European commission, 2000a). Landfilling can cause some problems as the incinerating (i.e. noise, dust and smell) (European commission, 2000d; Przewrocki et al., 2004; Fytili and Zabaniotou, 2008). Is also possible to use it as construction material, mixing the sludge with clay and then heat them up to 1.500ºC (Lin et al., 2012; Cuisdó and Cremaades, 2012). The resulting product is a clay brick that can be used in construction (Lin et al., 2012; Cusidó and Cremaades, 2012). There is also some concern about the possible health issues that the use of sludge as brick material can cause, due to the content of heavy metals (Cusidó and Cremaades, 2012). Some heavy metals such cadmium, chromium, arsenic, lead mercury and nickel are known to cause health problems when there is exposition to those materials, and that exposition can be cause by the gas emission and the leachates from those products, but the literature shows that the heavy metals emission by those processes are almost nothing (Cusidó and Cremaades, 2012). There are others concerns about the use of sludge as brick material, due to the possible loss of mechanical properties such as flexural strength resistance and compressive strength resistance, although the literature shows that there is a decrease in compressive strength resistance, they also show an increase in flexural strength resistance, in lightness and un thermal and acoustic isolation using bricks with 5-25% of sludge comparing to conventional clay bricks (Lin et al., 2012). 17 3.5. -Phosphorous in the soil and in sludge Phosphorous is one of the main elements in sludge, with a high level of 15% DM (Fytili and Zabaniotou, 2008), but this level of phosphorous can be high for agricultural application causing problems for instance eutrophication (Millier and Hooda, 2010). Environmental problems such eutrophication is caused due to the run-off of the available phosphorous. Other forms such as dissolved organic phosphorous and soluble reactive phosphorous can also be leached and contaminate ground-water (Miller and Hooda, 2010). Some of the un-available phosphorous that cannot be used by the plants and microorganisms in the current form can be converted into available phosphorous by the action of phosphatase, and enzyme that releases ortho-phosphate from the organic form (Xie et al., 2011). The high concentration of seaweed decreases the amount of light that enter in the water and they decrease the oxygen concentration in the water (Sostres, 2001). There is also off odors caused by the breakdown of the seaweeds and presence of harmful microbes that can cause diseases (Sostres, 2001). Phosphorous can precipitated in flooding environments such as in rice fields (Abolfazli et al., 2012). pH soil is considered the main factor that can determine the precipitation of the phosphorous. Ions such Ca, Al and Fe can act with phosphorous to form precipitated phosphorous compounds (Abolfazli et al., 2012). In alkaline soils, Ca precipitate is the dominant form. Fe and Al forms are insoluble under anaerobic conditions and are mainly form under acid conditions. Extractable Olsen phosphorous increases when the rate of fertilizer is increased (Wang et al., 2010). Application of organic fertilizers based on nitrogen needed for each species can lead to phosphorous accumulation in the soil due to the lower nitrogen: phosphorous ratio of the organic fertilizer (Kashem et al., 2010). There is a high level of the lost phosphorous due to increase of washing powders use and due to the change in nutrition and life style (industrialization process). Detergents are the main phosphorous source in municipal wastewater, since it contains high level of sodium tripolyphosphate (Rybicki, 1997). Some countries such as Switzerland have prevented the use of the detergents as a result of the eutrophication problems. Phosphorous can be removed by chemical process through the precipitation or by biological process (Rybicki, 1997). In the chemical process, it is common to use 18 aluminum salts or iron salts. However, sludge with biological treatment is usually more unstable and more odorous (Rybicki, 1997). There has been an excessive application of phosphorus in the fields. The estimated average of phosphorus that is added per year in excess is 19kg/ha (Breeuwsma et al., 1995). A big part of that problem is cause by the excessive use of phosphate fertilizers, but is also caused by the excessive manure application. Manure usually has N:P ratio much lower than which is needed by the plant, and as a result there is phosphorus accumulation (Sostres, 2001). Small part of organic phosphorous can be biologically active. Primary phosphorus minerals are slowly dissolves providing phosphate ion to the solution (Carpenter, 2005). A part of these ions will be precipitated as secondary phosphorous minerals and this is unavailable forms (Smil, 2000). Biomass phosphorous is the most active form and can be taken up by predators or saprophytes and incorporated to new consumers biomass (Smil, 2000). Mineralization of organic phosphorous occurs due to the action of an enzyme called phosphatase that can be produced by the microorganism or by the plants (Richardson 2001). Phosphorous mineralization is mainly mediated by bacteria such as Bacillus and Pseudomonas spp., fungi such as Penuicillium and Aspergillus spp. and protozoa such as Tetrahymena pyriformis (Barsdate, R. et al., 1974; Richardson 2001). Eutrophication is the process was the excessive grow of algae caused by the excessive nutrient content in the water, causing anoxia problems (Carpenter, 2005). Problems caused by eutrophication include purifying water cost to make the water available for humans, losses in wild life, problems of bad odors and reduction in fish population (Carpenter, 2005; Smil, 2000). One of the major causes of eutrophication is the high phosphorous content in the water that can be due to factories discharges to the rivers, run off from agricultural lands, sewages, construction sites and urban areas (Smil, 2000). For this reason, some countries have developed some regulations in factories and municipal discharges to the rivers. Agricultural land is one of the most important sources of phosphorous due to the excessive fertilization that leads to phosphorous accumulation in the soil, and can be then washed and remove from the soil by leaching or by run-off and finally accumulate in the lakes causing eutrophication (Carpenter, 2005). 19 Phosphorus enters in the soil as inputs in inorganic form when fertilizer, sludge or crop residues are incorporated to the soil (Smil, 2000) Organic phosphorus cannot directly be uptake by the plant roots. The microorganisms such as bacteria and protozoa can use this organic phosphorus. After it is used by these microorganisms, organic phosphorous can become an available form in the soil solution. Also, some part of the soluble phosphorous can precipitate with other elements such as calcium, iron or aluminum making it less available for the plant. But, such fractions of mineral forms can become solubilized again, making long-term phosphorus storage (Smil, 2000). Phosphorus end in the water by desorption, by dissolution or by removal, then there is the transport which is made by runoff or by deep rising (Sostres, 2001). Water of the rainfall is responsible of the that process, but the effect is minimized by the sorption of the soil (Sostres, 2001). When the water flux is made by the macropores, the phosphorus lost can be high (Sostres, 2001). High losses can be caused by having bad drainage or due to an excessive organic fertilization (Simard et al., 2000). Regarding the flux of phosphorus particles, is mostly caused by superficial erosion or soil erosion in drainage channels (Sostres, 2001). During this process there is a selection of phosphorus where the smallest particles are selected, and those particles are the ones that has higher sorption capacity and higher phosphorus content (Haygarth and Jarvis, 1999). In manure there is a higher rinsing of phosphorus due to the higher amount of organic phosphorus whose diester phosphate groups can be barely adsorbed by the soil surface (Sostres, 2001). 20 Figure 1. Phosphorus cycle Regarding phosphorus fractionation in sludge, there are some studies were they tried to find out how phosphorus fractionation was influenced by the sludge treatment. Choi et al. (2009) carried out a study in order to differentiate between the different phosphorus fractions that are present in sludge (biologically bound phosphorus and physiochemical bound phosphorus). They also differentiate in the physiochemical bound phosphorus between soluble phosphorus and adsorbed phosphorus. Moreover the adsorbed phosphorus was divided into the soluble reactive phosphorus and soluble nonreactive phosphorus. The experiment included different treatments (sludge with iron precipitation or sludge without iron precipitation). The results showed that iron precipitation decreased the biologically bound phosphorus, but it has not affected the 21 soluble fraction. In addition, the phosphorus bound to Al and Fe was quite high comparing to sludge without iron precipitation. Huang et al. (2012) conducted an experiment where they use sewage sludge treated with different chemicals (Fresh dewatered anaerobically digested sludge, stabilized with ferrous sulfate, stabilized with calcium oxide and stabilized with aluminum sulfate) to study the different phytoabailability of phosphorus in the different treatments. The fertilizer was highest in phytoavailability, followed by the aluminum sulfate and the dewatered and fresh sludge, while calcium oxide has less and ferrous sulfate. Criquet et al. (2007) studied the effect of sewage sludge application (aerobically and aerobically digested sludge). The sludge application resulted in an increase in the phosphorus content, phosphatase activity and microbial activity, but also the phosphatase activity was decreased over with the time. Xie et al. (2011) studied phosphatase activity and phosphorus fraction in sewage sludge. The results shows that the main fraction in sludge was the inorganic phosphorus and non-apatite inorganic phosphorus were the highest fractions. Phosphatase activity was high, and that can be one of the causes why inorganic phosphorus was the main fraction. 22 3.6. -Heavy metal concentration in sludge, and its effects in the soil. Probably the main strain of research in sludge issues is its heavy metal content, there is a lot of literature where they measure the different concentration of heavy metals in the sludge, and in some studies they also measured heavy metal content in the soil or in plants that have grown in soil fertilized using sludge. Goi et al. (2005) studied the heavy metals levels that are present in different sludges. Ten different samples from ten different wastewater plants were used for about 11 elemental analyses (Cd, Cr, Cu, Hg, Ni, Pb, Zn, Ba, Co, Mo and Mn). The results illustrated that these sludges contain lower heavy metal levels than the limits values that are established by the European Union. Nyamangara and Mzezewa (1999) studied the effect of sludge application on the long term (19 years) on Zn, Cu, Ni and Pb accumulation in the soil. The content of Zn, Pb, and Cu was highest in the upper layers of the soil. The results showed also that lowest content of the heavy metals in the lowest layers indicates that water contamination was very low comparing to run-off. Alonso et al carried out an experiment in 2005 where they measured the concentration of various elements (Al, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Ti and Zn) in anaerobic treated sludge. In small wastewater plants, anaerobic treatment is the most common. To make the digestion they used a mixture of 10 mL of nitric (HNO3), hydrochloric (HCl) and hydrofluoric acid (HF), in the ratio 5:4:1 to digest in the microwave 0,5g of sample. They also distinguished between exchangeable fraction, oxidizable fraction, reducible fraction and residual fraction. They couldn’t measure mercury content due to its lower fraction that was lower than the detection level of the ICP machine. Most of the elements had low percentage of exchangeable form, only cobalt (17%), manganese (35%), nickel (11%) and zinc (12%) had relatively high percentage of exchangeable form. Zinc and manganese again showed the highest rate of reducible form. Despite the already mentioned elements, all elements show a high percentage of oxidizable form, ranging from 20 to 40% and even higher the case of molybdenum (53%) and cobalt (61%). Finally the residual fraction was also high in most of the elements and represents fractions that are bound to the mineral matter of the 23 sludge. These results explained why cobalt, manganese, nickel and zinc are the most common elements analyzed in the literature and why their presence can cause toxicity problems in lower concentrations than in other elements. Doelsch et al made a research in 2006 where they evaluate the impact of sewage sludge in the tropical soils of the island of Reunion in the Indian Ocean. This island has a volcanic origin, and soils with volcanic origin have naturally higher content of heavy metals than other type of soils. Due to that they cannot legally apply sewage sludge in most of the soils. In the research they compare control fields fertilized by NPK and sewage sludge. They found out that Zinc had the highest mobility; nickel mobility was also high and much bigger than copper and cadmium. But there weren’t significant changes in the soil concentration of heavy metal after two year of sewage sludge application, but sewage sludge application increased the mobility of heavy metals. Ahlberg et al in 2006 studied the leachates and size of the particles that were leaching from a soil amended with sewage sludge at different times. They used a lysimeter to obtain the samples. The studied elements were Na, Ca, Mg, Mn, Sr, Zn, K, Li, Ni, Cd, Co, Rb, Ag, Cr, Ba, Cu, Ga, Al, Pb and Fe. They found out that the relative amounts of metals leached after one year, expressed as percent of total environmentally available content per kg DS of sludge, have the order: Na > Ca =Mg > Mn > Sr > Zn > K > Li = Ni > Cd > Co > Rb >Ag > Cr > Ba = Cu > Ga > Al = Pb = Fe. They also distinguished two groups of heavy metals, those that has a higher rate of leaching just after the application and then decreases, but there is another group (Zn, Cd, Mn, Ni, Sr, Ca, Al and Li) that have a cycling rate, being higher in colder months. They show that most of the elements leachated in particles smaller than 10 kDa, but other elements such as Fe, Al and Cr had important reduction in leachates rates (20-70%) when a filter of 0,45µm was used. Mattana et al in 2014 investigated the effect of three different types of sludge application (aerobic digested, aerobic digested + composted and aerobic digested + thermal threated) in the soil bacterial community. ATP activity was significantly higher in aerobic digested + composted sludge and aerobic digested + thermal threated sludge, which means that the microbial activity was higher in those sludge types. Sludge application enhanced in all cases enzymatic activity, but this increase was significantly higher in aerobic digested + thermal threated sludge. Community fingerprinting analysis 24 showed that there were genetic differences between bacterial communities of each sludge type. The authors link the higher bacterial activity and the higher concentrations of nutrients and heavy metals in aerobic digested + thermal threated sludge to the particle size reduction that enhance bacterial activity and as a result, enhance the availability of different elements. Cornu et al in 2001 carried out an experiment to estimate the potential consequences that sewage sludge can cause in ferralsols in Brazil. Ferrolitic soils are quite acid with pH lower than 5, with low content in nutrients and organic matter, those characteristics made them more vulnerable to sewage sludge applications. They analyzed the sludge, soil, drainage water and runoff water using 24 ton of sludge per hectare. Runoff had slightly higher concentrations of Cl, Ca, Cu, Ni and Pb when it was flowing in soils amended with sewage sludge. Drainage water increased its elements exports when they flow across soil amended with sewage sludge. Despite this increase of element transport when there is sludge application, the total average of element exported is still small. Soil characteristics didn’t change after sludge application, due to the nutrient export by the crop, and the existing high concentration of heavy metals which in comparison with the added by sewage sludge wasn’t significantly higher. 31 correlation between plant growth and nutrient availability. Although, the highest nutrient content was in soil treated with biosolids, but the high salinity of this material resulted in a decrease in the growth of the grass. Abolfazli et al. (2012) carried out an experiment to find out what are the effects of chemical phosphorus fertilization and organic fertilization in submerged soil. The study included 5 treatments (phosphorus fertilizer triple superphosphate, phosphorus fertilizer diamonnium phosphate, and cow dung manure and sewage sludge) to investigate the effect of these treatments on rice growth and production in acid soil and calcareous soil). The phosphorus fractions (available phosphorus, aluminum fraction, iron phosphorus and calcium phosphorus) were analyzed in the soil before and after the treatments. The results showed that organic fertilizers such as manure or sludge resulted in an increase in the available phosphorus. In addition, phosphorus bounded with Ca was the highest in calcareous soils, while the phosphorus bounded with aluminum and iron were the predominant forms. Singh and Agrawal (2007) investigated the effect of sewage sludge application as fertilizer for Beta vulgaris L. plants. The Cd contents in the soil where above the permissible level in India legislation, pH decreases and conductivity increases in the soil treated with sludge. Also Cd, Ni and Zn content in the plant were above the limit values that have been established by India government for this crop. The high content of such heavy metals resulted in a reduction in root length, leaf area, photosynthetic rate and chlorophyll content and an increase in lipid peroxidation activity and protein level. Seleiman et al. (2012) conducted an experiment to find out how sewage sludge application affects the quality and productivity of bioenergy crops. Different quantities of sludge were added to pots where maize and oilseed rapes were sown. The sludge application resulted in an increase in the leaf area and biomass accumulation, but it also increased the heavy metals content in plant biomass without adverse effect on plant growth. Hernández et al. (1990) investigated the effect of sludge and poultry manure application on the crop yield of maize and the availability of heavy metals in the soil. The results showed that sludge increased the yield and the N content, whereas K content in plant was lower than in plants fertilized with poultry manure. 32 Casado-Vela et al studied in 2007 in Alicante (Spain) the effect of increasing composted sludge application in the growth of sweet pepper (Capsicum annuum). They measured the nutrient, heavy metal content, pH and salinity in the water used for irrigation, in the composted sludge and in the soil. In most of the experiments they don´t measured the average content of heavy metals in water, but it can be an important source of those elements. They also made the experiment in two different places, in the open field and in the greenhouse. The four different treatments that they used were T1 = 0 kg m-2; T2 = 3 kg m-2; T3 = 6 kg m-2 and T4 = 9 kg m-2. They found out that there were an increase in conductivity as sludge was increasing, and there were also an increase of conductivity with the passage of time after sludge application due to the increasing solubilisation of its compounds. In addition there were differences between conductivity in open field and greenhouse, in the open field the conductivity was higher due to the higher temperature changes that enhance solubilization. Usually is consider that a conductivity increase higher than 3000 µS/cm lead to yield decreases, but even in the highest application rate (9 kg m-2) the conductivity only reached an increase of 1200 µS/cm. There weren’t changes in pH. Organic matter content was higher in the higher application rates, but in the greenhouse the increase was lower due to the higher mineralization rate caused by the higher temperature. As it was expected, there was a significant increase of phosphorus with the increasing application rate, but with the high pH (upper than 7) and high temperature there can be a precipitation of phosphorus into calcium phosphates. In addition, there were also an increase in soil concentration of Kjendahl nitrogen, sodium, potassium, calcium, iron, manganese, copper, zinc and boron, but there was a decrease in the concentrations after 200 days of growing due to the absorption by the plants. The highest yield and biggest fruits were found in the greenhouse using 9 kg m-2, but the negative effect that the continiuos applicatoin of that product can cause, allow to the authors to advice using a smaller application rate of 6 kg m-2. De Saavedra et al studied in Spain in 2000 where they sow maize using three different treatments of basal dressing, mineral fertilizer, 8.000 kg ha-1 of sludge compost (Mixture I) and 12.000 kg ha-1 (Mixture II). In all of them top dressing was 350 k ha-1 of urea. Yield was 10% higher in mixture I than in mineral fertilization, and if we compare with mixture II, yield was 20% higher. There weren’t changes in the pH of the 33 soil and there was an small increase in the electrical conductivity in all of the treatments. After sludge application there is an increase in the concentration of heavy metals, but it was still below the established limit by the Spanish and European legislation. A study made by Vasseur et al in Quebec (Canada) in 2000, tried to find out the effect of countiuos sewage sludge application in the biodiversity, yield, weeds and chemical characteristics of the soil. The studied soil was well drained loam, clasify by the FAO as Podzols. The used sludge was biologically treated during 21 days in places with similar farming practices and crops, same area, growing hay for animal feeding and plowing after harvest. The total amount of sludge appied varied from 1,3 to 9,4 Mg DM ha-1. The dry matter content was really low, ranging from 2,5% to 13,2% so as to be applied by sprayers. There was also a different treatment using composted sludge that was applied with higher dry matter content (44,7%), and had much higher pH, 12,3 comparing to the 6,2-6,9 of sewage sludge. Results showed that diversity index varied from place to place, due to the differences in the grown species by farmers and the edafic differences, but there were also significant differences in two places were the not treated fields showed higher diversity index than the treated field. Usally weeds have higher tolerances to high concentration of heavy metals, so they could adapt better to the sludge application, but in that study there were no significant differences between not treated fields and sludge treated fields. Regarding soil composition there were no significant differences in their chemical characteristics in sludge treated soils and not treated soils. De Imperial et al investigated in 2002 in Spain the differences in the emergence of six crops using composted sludge, not composted sludge and control under greenhouse conditions. They used Tomato (Lycopersicon esculentum Mill.), spinach (Spinacia oleracea L.), lentil (Lens esculenta Moench), maize (Zea mays L.), wheat (Triticum aestivum L.), and ryegrass (Lolium perenne L.) for the experiment. Application ranges were 0 ton ha-1, 40 ton ha-1 and 80 ton ha-1. They measured the amount of emerged plants, stem length and root length. The results shows that there were significantly higher values of all of the measure characteristics with 40 ton ha-1 of composted sludge in all plants excepting Lens esculenta, where the highest values were found using 40 ton ha-1 of fresh sewage sludge. The difference was attributed by the authors to the higher 34 sentitive of Lens esculenta to salinity increases, and fresh sewage sludge has lower salinity than composted sludge. In India is quite difficult to find fresh water to be further used in irrigation, that’s why is usual to use sewage effluents as a water source for irrigation. Rattan et al studied in 2005 the effect that this practice can have on the soil. They made a chemical analysis of sludge used in irrigation, ground water, soil and plants (Oryza sativa L., Triticum aestivum L., Shorgum vulgare Pers., Zea mays L., Avena sativa L., Brassica napus L., Brassica campestris L., Spinacea oleracea L., Cucumis sativus L., Raphanus sativus L. and Trifolium alexandrium L. They found out that the sewage sludge used in irrigation just had slightly higher concentration of heavy metals than groundwater, and even the same in cases like Pb and Cd. Regarding nutrients like P, K and S, the concentration were various folds higher in sewage sludge than in groundwater. All the sludge samples were below the limit established by the Indian irrigation recommendations made by the Ministry of Agriculture. Only conductivity exceeded the recommendations by 1 dS m-1. As a result of sewage sludge application they measured an increase in heavy metal concentration in the soil irrigated using sewage sludge. Heavy metal content in plants varied between species, in the case of Oryza sativa there were high accumulation of Zn and Cu. In Triticum aestivum the increase was higher in Zn, Cu, Fe, Mn and Ni. Shorgum vulgare accumulates higher amounts of Fe, Cu and Ni. Avena sativa and Raphanus sativus only showed increases in Mn concenctration. Spinacea oleracea has higher amounts of Zn, Cu and Ni. In the rest of the plants the results didn’t have enough significance to allow conclusions about them. Despite the increase in heavy metals concentration any of them had enough concentration to cause phytotoxcity effects. Ramirez et al tried to find out in 2008 the toxic effects of digested sludge, composted sludge, thermally dried sludge and pig slurry in three different plants (Brassica rapa, Lolium perenne and trifolium pratense). To do that, they made a seedling test using the reduction in emergence rate as a measure of toxicity. The results showed that composted sludge inhibit less germination than fresh sludge or thermally dried sludge. To reach the total inhibition they needed 20 g kg-1 in pig slurry, 50 g kg-1 in not composted sludge, 151 g kg-1 in thermal treated sludge and 300 g kg-1 in composted sludge. This study shows a clear negative correlation between sludge stability and toxicity. The authors 35 suggested that phytotoxicity was mediated by the release of ammonium, phenols, and organic acids during waste degradation. Seleiman et al carried out and experiment in 2014 in Finland where they measured the concentration of different elements in maize, oilseed rape and hemp fertilized with high dose of sewage sludge and low dose of sewage sludge. They obtained the different extraction made by those plants. Table 6. Heavy metal extraction by maize, oilseed rape and hemp at different dose of sludge. Specie As mg kg-1 Cd mg kg-1 Cr mg kg-1 Cu mg kg-1 Ni mg kg-1 Zn mg kg-1 High dose Maize 1,72 0,06 10,55 5,6 0,98 85,5 Oilseed rape 0,05 0,05 0,12 2,5 0,22 19,5 Fiber hemp 0,07 0,05 0,28 6,7 1,68 38,0 Low dose Maize 1,55 0,05 10,43 5,9 0,97 79,3 Oilseed rape 0,05 0,06 0,13 2,4 0,22 13,5 Fiber hemp 0,07 0,05 0,14 6,0 1,22 31,3 Specie Cl g kg-1 K g kg-1 S g kg-1 Si g kg-1 C g kg-1 N g kg-1 High dose Maize 1,9 3,1 1,23 1,36 426 15,0 Oilseed rape 2,1 3,4 4,87 0,24 422 5,5 Fiber hemp 2,2 7,0 2,99 5,60 408 13,8 Low dose Maize 1,6 3,3 1,29 1,13 427 15,0 Oilseed rape 2,0 2,8 4,46 0,27 423 5,0 Fiber hemp 2,2 8,0 1,81 4,77 424 10,9 36 37 4. Research objectives The overall objective is to quantify the nutrients and heavy metals from sewage sludge and calculate the dose of these products can be applied to crops. The specific objectives are considered: Perform a chemical analysis of sludge from water treatment plants as well as sludge from cow farms. Compare the chemical properties of both products and analyze if the studied sludge can be legally used for agriculture proposes according to three different legislations: European Directive (91/271/EEC), Spanish legislation (Minesterio de Agricultura, Pesca y Alimentación, 1310/1990) and Finnish legislation (Ministry of Agriculture and Forestry, 282/1994). Make the dosage of sludge and manure for fertilization, firstly based on the legal limitation of heavy metal concentration and total amount of heavy metals applied to the soil per year. Then it will be based on the main nutrient extractions (nitrogen, phosphorus and potassium) and it will be evaluated the effect in the nutrient balance for a three year period. Finally it will be discuss which the best legally possible fertilization plan is for a three year period using maize, oilseed rape and hemp (all for biomass production) as crop rotation. 38 39 5. -Material and methods Seven different products of sewage sludge were collected from different places, Finland (Viikki (urban distrit of Helsinki, 100.000.000 m3 of waste water per year, 608.000 habitants), Forssa (17.700 habitants), Vaasa (57.200 habitants), Jyvaskyla (132.000 habitants), Kauvula (87,300 habitants), Maanika (cow farm), Kalmari (cow farm)). Only sludge collected from Kalmari and Maaninka was from dairy cows, which was in a liquid form before it was centrifuged to obtain the solid part for the analysis. No any treatments have been done on sludge collected from dairy cows. The biological treatments was used in the sludge production obtained from Forssa, while chemical treatments were used during the production process of sludge collected from Viikki (Helsinki), Jyvaskyla, Vaasa, Kauvula. All samples were randomly taken from the trailer that was used to transport and then homogenized. The samples were collected by university workers the 22th of November of 2013. Figure 4. Region where the samples were obtained. 40 Figure 5. Sample locations. 1: Forssa; 2: Jyväskylä; 3: Kouvola; 4: Vaasa; 5: Viikki (Helsinki); 6: Kalmari; 7: Maanika. Soil samples were taken from a field in Viikki (Helsinki, Finland), Coordinates 60.224301,25.024950, owned by the Department of Agricultural Sciences, Helsinki University the 24th of March of 2014. Four samples were collected from 4 different random places of the field. The sample was taken from the first 50cm and then homogenized. Figure 6. Field location. 47 finally 5 min of ventilation at 0 W was applied. After the extraction, the vessels were allowed to cool at room temperature before they were opened. After the digestion, the samples were filtered and diluted with distillated water up to 50 mL. Then they were kept in the storage room overnight in cold room at -5 ºC. Finally the measure was made by Inductively Coupled Plasma-Optical Emission Spectrometry (iCAP 6200, Thermo Fisher Scientific, Cambridge, UK). To make the measured it was necessary to make three different standard solutions to be able to make the calibration of different concentrations. The standard solutions are summarized in the following table: Table 7. Standard solution I for ICP analysis. S1 S2 S3 S4 S5 mg L-1 mg L-1 mg L-1 mg L-1 mg L-1 Al 2 12,5 25 50 100 Ca 2 25 50 100 200 Fe 2 25 50 100 200 K 2 5 10 50 100 Mg 2 5 10 50 100 Zn 2 5 10 50 100 Na 2 5 10 As 2 5 10 Hg 2 5 10 48 Table 8. Standard solution II for ICP analysis. S6 S7 S8 S9 S10 mg L-1 mg L-1 mg L-1 mg L-1 mg L-1 As 0,01 0,05 0,1 0,5 1 Hg 0,01 0,05 0,1 0,5 1 Al 0,01 0,05 0,1 0,5 1 B 0,01 0,05 0,1 0,5 1 Ca 0,01 0,05 0,1 0,5 1 Cd 0,01 0,05 0,1 0,5 1 Cr 0,01 0,05 0,1 0,5 1 Cu 0,01 0,05 0,1 0,5 1 Fe 0,01 0,05 0,1 0,5 1 K 0,01 0,05 0,1 0,5 1 Mg 0,01 0,05 0,1 0,5 1 Mn 0,01 0,05 0,1 0,5 1 Na 0,01 0,05 0,1 0,5 1 Ni 0,01 0,05 0,1 0,5 1 Pb 0,01 0,05 0,1 0,5 1 Zn 0,01 0,05 0,1 0,5 1 P 0,5 1 49 Table 9. Standard solution III for ICP analysis. S11 S12 S13 S14 S15 mg L-1 mg L-1 mg L-1 mg L-1 mg L-1 P 2 25 50 100 200 Si 0,1 1 10 25 50 S 0,1 1 10 25 50 Using these standard solutions the machine was able to measure the following range of concentrations: Table 10. Limit precision ranges. Al As Mn Cd Cr Cu Pb Ni mg kg-1 10006500 1-5 60-220 0,4 10-30 90-270 5-20 5-20 Zn Hg K Ca Mg P S Si mg kg-1 130470 0,5 2100 38000 3300 10 00026000 1001800 950036000 All reagents were of analytical-reagent grade. The water used in the dilution was deionized and it was purified using Millipore (Bedford, MA, USA) Milli-Q system. Aqueous stock solutions of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn, S, Si, Mg, K and Na were prepared by dilution of the respective standard 1000 mg L-1 solutions (Merck, Germany). All standard and reagent solutions were stored in polyethylene bottles. 50 Figure 12. Sludge prepared for microwave digestion. Figure 13. ICP analysis machine. 51 5.1.5. -Nitrogen and carbon content and ratio Nitrogen and carbon content was analyzed using Dumas combustion method (Etheridge et al., 1998). In this method, dried samples (500 mg) from oven and air drying were milled using a mortar and then put into Vario MAX CN (Elemental Analyze system GmbH, Hanau, Germany). 5.1.6. -Statistical analysis All of the physico-chemical analyses were repeated four times for phosphorus fraction, dry matter, nitrogen content, carbon content, CN ratio, salinity and pH, and for ICP the analysis was repeated six times using independent samples from each sub-plot corresponding to sludge from Viikki, Forssa, Vaasa, Jyvaskyla and Kauvula, cattle manure from Mannika, Kalmari, and soil from a field in Viikki. ANOVA statistical analyses of data at 95% significance were carried out. Significant statistical differences, as F-values, among means are shown as different letter (a, b, c, d, e). The values of means were compared with each other through Duncan’s multiple range test. Data manipulation was performed with Microsoft Excel and PASW statistics v. 18. (IBM Inc., Chicago, IL, USA). 5.2. -Evaluation of sludge of agricultural use 5.2.1. -Legal requirements To evaluate if it is legally possible to use the analyzed sludge samples, there will be done three analyses: 1Soil characteristics will be compared with the limit values established in the European Directive, in the Spanish legislation and in the Finnish legislation. 2Sludge characteristics will be compared with the limit values established in the European Directive, in the Spanish legislation and in the Finnish legislation. 52 3Maximum amount of sludge that can be used for the studied soil will be calculated according to the European Directive, the Spanish legislation and the Finnish legislation. For that propose there will be used the following equation: ( ) ( ) ( ) 5.2.2. -Fertilization dosage All calculation will be done for a three year period, using a rotation with maize, oilseed rape and hemp. The expected yield data will be obtained by from the study done by Seleiman et al in 2013. To calculate the dosage of the sludge, nutrients extractions of maize, oilseed rape and hemp made by Seleiman et al in 2014 will be used. For micronutrients (As, Cd, Cr, Cu, Ni and Zn) the following equation will be used. ( ) ( ) ( ) For macronutrients (C, N, P, K, S and Si) there will be used: ( ) ( ) ( ) The total amount of nutrient extracted by the successive crops will be calculated as the sum of each crop extraction, represented in the following equation: ( ) ∑ ( ) Then, to calculate the dosage there will be used three hypothesis: 1Using Nitrogen extraction: ( ) ( ) ( ) 53 2Using Phosphorus extraction: ( ) ( ) ( ) 3Using Potassium extraction: ( ) ( ) ( ) 5.2.3. -Final nutrient balance Finally there will be calculated the resulting nutrient balance in the soil. To do that first there will be calculated the amount of nutrient that is incorporated by the dosage (previously calculated for N, P and K dosages). ( ) ( ) ( ) Then there will be calculated nutrient extraction by the crop using: ( ) ( ) ( ) Total extraction will be calculated by: ( ) ∑ ( ) Balance will be obtained by: ( ) ( ) ( ) 54 6. -Results 6.1. -Chemical characterization of the soil The soil was slightly acidity with a pH of 6.05. There were no salinity problems because the conductivity was low (0.17 ds m-2). P fractions in the soil showed how most of the P was presented in the secondary phosphorus minerals (Al-P, Fe-P and Ca-P), and the highest precipitated P was with the aluminum (0.66 g kg-1). The lowest fraction of P was the soluble form. The soluble form was account for about 5%, while the P bounded with Al was accounted for 44% of the total P. Table 11. Chemical and physical characterization of the soil Soil Standard desviation Dry matter % 98.06 0,05 Moisture % 1.94 0,05 pH 6.05 0,10 EC ds m-1 0.17 0,01 N g kg-1 1.99 0,08 C g kg-1 25.43 1,89 C:N ratio 12.81 1,32 Soluble P g kg-1 0.08 0,00 Al-P g kg-1 0.66 0,02 Fe-P g kg-1 0.41 0,03 Ca-P g kg-1 0.34 0,01 Total P g kg-1 1.48 0,04 55 Table 12. ICP analysis of the soil: Mean Standard deviation Al mg kg-1 1.473,27 16,77 As mg kg-1 1,71 0,11 Ca mg kg-1 9.606,75 3.790,30 Cd mg kg-1 0,11 0,01 Cr mg kg-1 7,56 0,16 Cu mg kg-1 7,87 0,12 K mg kg-1 10.505,68 20,81 Fe mg kg-1 150,13 1,78 Mg mg kg-1 109,16 1,25 Mn mg kg-1 7,63 0,36 Na mg kg-1 17,49 0,58 Ni mg kg-1 3,18 0,17 P mg kg-1 16.375,90 158,28 Pb mg kg-1 8,30 0,62 S mg kg-1 7,77 0,31 Si mg kg-1 384,61 6,06 Zn mg kg-1 31,87 2,42 56 6.2. -Chemical characterization of sludge and manure. Table 13. Dry matter content in sewage sludge (S) and manure (M). Sludges N Mean Std. Deviation Forssa (S) 3 27,98b 0,61 JKL (S) 3 29,80a 0,46 Kouvula (S) 3 29,38ab 0,18 Vaasa (S) 3 29,50a 0,30 Viikki (S) 3 30,29a 0,62 Kalmari (M) 3 10,71d 0,14 Maanika (M) 3 12,48c 0,90 Different letters indicates differences with a significance of 95%. As we can see in the results, moisture was quite higher in dairy cattle sludge comparing to sewage sludge from water treatment plants (Table 13). Between manure samples there were significant differences, being Kalmari the sample with lowest dry matter content. 63 Table 20. Carbon content in sewage sludge (S) and manure (M). Sludge N Mean g kg-1 Std. Deviation g kg-1 Forssa (S) 4 267,54b 32,20 JKL (S) 4 251,67b 9,31 Kouvula (S) 4 258,46b 4,23 Vaasa (S) 4 270,62b 10,24 Viikki (S) 4 245,07b 13,54 Kalmari (M) 4 376,29a 29,64 Maanika (M) 4 380,81a 25,76 Different letters indicates differences with a significance of 95%. Carbon content was significant higher in manure than in sludge (Table 20). 64 Table 21. CN ratio in sewage sludge (S) and manure (M). Suldges N Mean Std. Deviation Forssa (S) 4 10,06c 0,48 JKL (S) 4 7,11e 0,08 Kouvula (S) 4 9,36cd 0,13 Vaasa (S) 4 8,99cd 0,17 Viikki (S) 4 8,30de 0,18 Kalmari (M) 4 12,50b 1,18 Maanika (M) 4 16,80a 1,05 Different letters indicates differences with a significance of 95%. Regarding CN ratio, we can see that Jyvaskyla had the significant lowest CN ratio (Table 21). Manure had significant differences with sludge, but they also showed significant differences between each other, being higher in Maanika (Table 21). 65 Table 22. Electrical Conductivity in sewage sludge (S) and manure (M). Sludge N Mean dS m-1 Std. Deviation dS m-1 Forssa (S) 3 5,42c 0,14 JKL (S) 3 3,58d 0,03 Kouvula (S) 3 5,02c 0,41 Vaasa (S) 3 3,33de 0,10 Viikki (S) 3 2,90e 0,30 Kalmari (M) 3 7,51a 0,20 Maanika (M) 3 6,84b 0,12 Different letters indicates differences with a significance of 95%. The highest values of EC was found in sludge obtained from Kalmari, while the lowest values of EC were found in sludge obtained from Viikki and Forssa (Table 22). There were significant differences between sludge and manure, but also there were significant differences between each sample (Table 22). 66 Table 23. pH in sewage sludge (S) and manure (M). Sludge N Mean Std. Deviation Forssa (S) 3 7,73c 0,01 JKL (S) 3 6,91e 0,01 Kouvula (S) 3 7,50d 0,02 Vaasa (S) 3 6,98e 0,01 Viikki (S) 3 7,48d 0,05 Kalmari (M) 3 8,62a 0,05 Maanika (M) 3 8,41b 0,01 Different letters indicates differences with a significance of 95%. The pH was higher in the dairy cow manure obtained from Manninka and Kalmari than sludge obtained from other places (Table 23). Moreover there were significant differences between sludge and manure, being higher in manure (Table 23). Despite the variation in pH from sample to sample, all of them were neutral or slightly basic (Table 23). 67 Table 24. Aluminum content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 4.498,11cd 30,62 JKL (S) 6 4.587,26b 14,26 Kouvula (S) 6 4.527,45c 29,03 Vaassa (S) 6 4.672,11a 8,77 Viikki (S) 6 4.492,27d 8,94 Kalmari (M) 6 898,15e 15,02 Maanika (M) 6 902,15e 1,20 Different letters indicates differences with a significance of 95%. Aluminum content was significant lower in manure than in sludge, but there also were significant differences between each sludge sample (Table 24). In addition, aluminum content in manure is not precise due to its low content, below the precision limit of 1000 mg kg-1 (Table 10). 68 Table 25. Arsenic content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 4,73b 0,50 JKL (S) 6 4,86b 0,22 Kouvula (S) 6 4,96b 0,18 Vaassa (S) 6 4,99b 0,13 Viikki (S) 6 4,87b 0,26 Kalmari (M) 6 6,30a 0,32 Maanika (M) 6 6,50a 0,22 Different letters indicates differences with a significance of 95%. Arsenic content was significant higher in manure than in sludge (Table 15). Moreover manure concentrations weren´t very precise because they were over the precision limit of 5 mg kg-1 (Table 10). 69 Table 26. Calcium content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 38.559,64a 96,57 JKL (S) 6 38.362,00b 35,10 Kouvula (S) 6 38.372,96b 14,62 Vaassa (S) 6 38.537,84a 19,61 Viikki (S) 6 38.437,08b 47,84 Kalmari (M) 6 3.236,47c 42,16 Maanika (M) 6 3.268,41c 4,31 Different letters indicates differences with a significance of 95%. Manure had significant lower content of calcium than sludge (Table 26), but calcium content in sludge samples wasn’t precise due to its high concentration that was over the precision limit of 38.000 mg kg-1 (Table 10). 70 Table 27. Cadmium content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 0,40a 0,05 JKL (S) 6 0,43a 0,04 Kouvula (S) 6 0,46a 0,04 Vaassa (S) 6 0,40a 0,06 Viikki (S) 6 0,44a 0,05 Kalmari (M) 6 0,44a 0,03 Maanika (M) 6 0,46a 0,05 Different letters indicates differences with a significance of 95%. There wasn´t significant differences between samples (Table 27). All values were over the precision limit of 0,40 mg kg-1, but they were very near to it (Table 10). 71 Table 28. Chromium content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 30,61c 0,35 JKL (S) 6 31,65b 0,31 Kouvula (S) 6 31,41b 0,20 Vaassa (S) 6 30,46c 0,21 Viikki (S) 6 31,59b 0,30 Kalmari (M) 6 41,86a 0,23 Maanika (M) 6 41,82a 0,25 Different letters indicates differences with a significance of 95%. Manure had significant higher concentration of chromium than sludge (Table 28). But these results aren’t precise due to its high content in chromium, upper the precision limit of 30 mg kg-1 (Table 10). 72 Table 29. Copper content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 271,22a 0,37 JKL (S) 6 271,05a 0,50 Kouvula (S) 6 271,63a 0,31 Vaassa (S) 6 271,52a 0,57 Viikki (S) 6 272,89a 0,90 Kalmari (M) 6 39,74c 3,90 Maanika (M) 6 48,16b 1,23 Different letters indicates differences with a significance of 95%. Copper concentration was significant lower in manure than in sludge, but there were also significant differences between both manure samples, being lower in Maanika (Table 29). Is also remarkable that all the values were out of the precision range of 90270 mg kg-1 (Table 10). 79 Table 36. Lead content in sludge and manure. Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 19,63b 1,03 JKL (S) 6 20,53b 0,65 Kouvula (S) 6 19,94b 0,41 Vaassa (S) 6 19,76b 0,78 Viikki (S) 6 20,58b 0,84 Kalmari (M) 6 26,00a 0,99 Maanika (M) 6 26,82a 0,83 Different letters indicates differences with a significance of 95%. Lead concentration was significantly higher in manure than in manure (Table 36). Some of those results weren´t precise, because there were slightly above the precision limit of 20 mg kg-1 (Table 10). 80 Table 37. Sulfur content in sludge and manure. Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 82,73ab 2,48 JKL (S) 6 81,59ab 1,41 Kouvula (S) 6 80,55b 1,65 Vaassa (S) 6 84,67a 2,59 Viikki (S) 6 82,33ab 1,83 Kalmari (M) 6 32,27c 1,06 Maanika (M) 6 30,32c 1,38 Different letters indicates differences with a significance of 95%. Sulfur content was significantly higher in sludge than in manure, moreover there were some significant differences between sludge samples (Table 37). All samples were below the precision limit of 100 mg kg-1 (Table 10). 81 Table 38. Silicon content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 16.071,20a 49,03 JKL (S) 6 16.052,72a 39,15 Kouvula (S) 6 16.048,23a 36,58 Vaassa (S) 6 16.074,00a 21,28 Viikki (S) 6 16.077,25a 25,08 Kalmari (M) 6 3.041,79b 1.548,40 Maanika (M) 6 4.041,36b 1,96 Different letters indicates differences with a significance of 95%. Manure had significantly lower content of silicon than sludge (Table 38). But is should be said that silicon content in manure was significantly below the precision limit of 9500 mg kg-1 (Table 10). 82 Table 39. Zinc content in sewage sludge (S) and manure (M). Sludges N Mean mg kg-1 Std. Deviation mg kg-1 Forssa (S) 6 200,44a 22,72 JKL (S) 6 210,83a 15,63 Kouvula (S) 6 220,34a 18,50 Vaassa (S) 6 200,20a 28,89 Viikki (S) 6 210,21a 19,84 Kalmari (M) 6 29,57b 0,83 Maanika (M) 6 29,95b 2,37 Different letters indicates differences with a significance of 95%. Zinc content was significantly higher in sludge than in manure (Table 39). But in the case of manure, the values didn`t have much precision because their concentration was below the precision limit (Table 10). There wasn`t enough mercury in the samples to be appreciated by the equipment. 83 6.3. -Nutrient extraction by each crop According to the results obtained by Seleiman et al in 2014, the extraction of the crops are: Table 40. Nutrient extractions of different crops. Maize Oilseed rape Hemp Yield (kg ha-1) 25.000 10.000 15.000 As (mg ha-1) 43.000 500 1.050 Cd (mg ha-1) 1.500 500 750 Cr (mg ha -1) 263.750 1.200 4.200 Cu (mg ha -1) 140.000 25.000 100.500 Ni (mg ha -1) 24.500 2.200 25.200 Zn (mg ha -1) 2.137.500 195.000 570.000 Cl (g ha -1) 47.500 21.000 33.000 K (g ha -1) 77.500 34.000 105.000 S (g ha -1) 30.750 48.700 44.850 Si (g ha -1) 34.000 2.400 84.000 C (g ha -1) 10.650.000 4.220.000 6.120.000 N (g ha -1) 375.000 55.000 207.000 P (g ha-1) 24.500 30.200 92.000 As we can see in this table, there are differences in the nutrient extraction of the different crops. In all the nutrients, excepting sulfur, maize extracts higher amount of nutrients. In contrast, oilseed rape extracts lower amounts of nutrients (Table 50). 84 6.4. -Legal requirements 6.4.1. -Soil characteristics. According to the legislation, sludge can only be applied in soil where the concentrations of cadmium, chromium, copper, mercury, nickel, lead and zinc are below the legal limits. Comparing the results from ICP analysis with European legislation (86/278/EEC), Spanish legislation (Minesterio de Agricultura, Pesca y Alimentación, 1310/1990) and Finnish legislation (Ministry of Agriculture and Forestry, 282/1994), we can say that this soil can be fertilized using sludge. Table 41. Legal limitation for heavy metal concentrations in the soil. European Union Spain Finland Target soil Legal Cd mg kg-1 1-3 1 0,5 0,11 Yes Cr mg kg-1 - 100 200 7,56 Yes Cu mg kg-1 50-140 50 100 7,87 Yes Hg mg kg-1 1-1.5 1 0,2 - Yes Ni mg kg-1 30-75 30 60 3,18 Yes Pb mg kg-1 50-300 50 60 8,3 Yes Zn mg kg-1 150-300 150 150 31,87 Yes 85 6.4.2. Legal heavy metal concentration in sludge and manure. To be able to be legally used in agriculture, sludge must fulfill heavy metals concentrations set by the European Union and the member country (Finland and Spain in this case). Table 42. Legal limitation in heavy metal concentration in Forssa (S). European Union Spain Finland Forssa Legal Cd mg kg-1 20-40 20 1,5 0,4 Yes Cr mg kg-1 - 150 300 30,61 Yes Cu mg kg-1 1000-1750 1.000 600 271,22 Yes Hg mg kg-1 16-25 1,5 2 - Yes Ni mg kg-1 300-400 112 100 20,58 Yes Pb mg kg-1 750-1200 300 100 19,63 Yes Zn mg kg-1 2500-4000 450 1500 200,44 Yes Sewage sludge from Forssa can be legally used for agriculture proposes (Table 42). 86 Table 43. Legal limitation in heavy metal concentration in Jyväskylä (S). European Union Spain Finland JKL Legal Cd mg kg-1 20-40 20 1,5 0,43 Yes Cr mg kg-1 - 150 300 31,65 Yes Cu mg kg-1 1000-1750 1.000 600 271,22 Yes Hg mg kg-1 16-25 1,5 2 - Yes Ni mg kg-1 300-400 112 100 25,84 Yes Pb mg kg-1 750-1200 300 100 20,53 Yes Zn mg kg-1 2500-4000 450 1500 210,83 Yes Sewage sludge from Jyväskylä can be legally used for agriculture proposes (Table 43). Table 44. Legal limitation in heavy metal concentration in Kouvula (S). European Union Spain Finland Kouvula Legal Cd mg kg-1 20-40 20 1,5 0,46 Yes Cr mg kg-1 - 150 300 31,41 Yes Cu mg kg-1 1000-1750 1.000 600 271,63 Yes Hg mg kg-1 16-25 1,5 2 - Yes Ni mg kg-1 300-400 112 100 20,1 Yes Pb mg kg-1 750-1200 300 100 19,94 Yes Zn mg kg-1 2500-4000 450 1500 220,34 Yes Sewage sludge from Kouvula can be legally used for agriculture proposes (Table 44). 87 Table 45. Legal limitation in heavy metal concentration in Vaasa (S). European Union Spain Finland Vaassa Legal Cd mg kg-1 20-40 20 1,5 0,4 Yes Cr mg kg-1 - 150 300 30,46 Yes Cu mg kg-1 1000-1750 1.000 600 271,52 Yes Hg mg kg-1 16-25 1,5 2 - Yes Ni mg kg-1 300-400 112 100 33,55 Yes Pb mg kg-1 750-1200 300 100 19,76 Yes Zn mg kg-1 2500-4000 450 1500 200,2 Yes Sewage sludge from Vaassa can be legally used for agriculture proposes (Table 45). Table 46. Legal limitation in heavy metal concentration in Viikki (S). European Union Spain Finland Viikki Legal Cd mg kg-1 20-40 20 1,5 0,44 Yes Cr mg kg-1 - 150 300 31,59 Yes Cu mg kg-1 1000-1750 1.000 600 272,89 Yes Hg mg kg-1 16-25 1,5 2 - Yes Ni mg kg-1 300-400 112 100 20,22 Yes Pb mg kg-1 750-1200 300 100 20,58 Yes Zn mg kg-1 2500-4000 450 1500 210,21 Yes Sewage sludge from Viikki can be legally used for agriculture proposes (Table 46). 88 Manure is not regulated by that legislation but it will be just compared with the same legislation as sludge, to see if they would fulfill the legal requirements that sludge has to complete. Table 47. Comparison with sludge legal limitation in heavy metal concentration. Manure from Kalmari. European Union Spain Finland Kalmari Legal Cd mg kg-1 20-40 20 1,5 0,44 Yes Cr mg kg-1 - 150 300 41,86 Yes Cu mg kg-1 1000-1750 1.000 600 39,74 Yes Hg mg kg-1 16-25 1,5 2 - Yes Ni mg kg-1 300-400 112 100 148,69 No Pb mg kg-1 750-1200 300 100 26 Yes Zn mg kg-1 2500-4000 450 1500 29,57 Yes If manure would has been included in sewage sludge legislation, this sample couldn’t be used for agriculture proposes, due to its high nickel content (Table 47). 95 As it was done in the legal limit for heavy metals content, manure will be compared with the application limits established in the legislation to study the maximum amount of manure that could be applied in the soil if it would be included in sludge legislation. Table 54. Maximum amount of sludge that can be applied on the soil according to its heavy metal content in Kalmari (M). Accumulation kg ha-1 Maximum amount of sludge kg ha-1 European Union Spain Finland European Union Spain Finland Cd 0,15 0,15 0,0015 340.909,09 340.909,09 3.409,09 Cr - 3 0,3 - 71.667,46 7.166,75 Cu 12 12 0,6 301.962,76 301.962,76 15.098,14 Hg 0,1 0,1 0,001 - - - Ni 3 3 0,1 20.176,21 20.176,21 672,54 Pb 15 15 0,1 576.923,08 576.923,08 3.846,15 Zn 30 30 1,5 1.014.541,77 1.014.541,77 50.727,09 In contrast with sludge, the higher limitation is in nickel content (Table 54). According to the European and Spanish legislation, the maximum amount of manure that could be applied is 20.176,21 kg ha-1 year-1 (Table 54). In Finland, with its more restrictive legislation, the maximum amount of manure that can be legally used is 672,54 kg ha-1 year-1(Table 54). 96 Table 55. Maximum amount of sludge that can be applied on the soil according to its heavy metal content in Maanika (M). Accumulation kg ha-1 Maximum amount of sludge kg ha-1 European Union Spain Finland European Union Spain Finland Cd 0,15 0,15 0,0015 326.086,96 326.086,96 3.260,87 Cr - 3 0,3 - 71.736,01 7.173,60 Cu 12 12 0,6 249.169,44 249.169,44 12.458,47 Hg 0,1 0,1 0,001 - - - Ni 3 3 0,1 20.307,32 20.307,32 676,91 Pb 15 15 0,1 559.284,12 559.284,12 3.728,56 Zn 30 30 1,5 1.001.669,45 1.001.669,45 50.083,47 In contrast with sludge, the higher limitation is in nickel content (Table 55). According to the European and Spanish legislation, the maximum amount of manure that could be applied is 20.307,32 kg ha-1 year-1 (Table 55). In Finland, with its more restrictive legislation, the maximum amount of manure that can be legally used is 676,91 kg ha-1 year-1(Table 55). 97 6.5. -Fertilization dosage 6.5.1. -Fertilization dosage according to Nitrogen extractions Using Nitrogen extraction to make fertilization dosage, the dosages are: Table 56. Nitrogen extractions of Maize, oilseed rape and hemp. Maize Oilseed Hemp Total N (g ha-1) 375.000 55.000 207.000 637.000 Nitrogen extraction has been calculated according to the extractions during three years of cropping, using the rotation of maize, oilseed rape and hemp, without considering losses by lixiviation and run-off. Table 57. Sludge and manure dosage according to nitrogen extraction (as dry matter). Dry matter Dosage kg ha-1 Forssa (S) 24.001,51 JKL (S) 17.989,27 Kouvula (S) 23.063,00 Vaasa (S) 21.162,79 Viikki (S) 21.578,59 Kalmari (M) 21.134,70 Maanika (M) 28.086,42 All those dosages are referred to dry matter, to calculate the real application dosage it must be divided by its dry matter content. 98 Table 58. Sludge and manure dosage according to nitrogen extraction (as fresh). Fresh Dosage kg ha-1 Forssa (S) 85.780,95 JKL (S) 60.366,68 Kouvula (S) 72.031,28 Vaasa (S) 71.643,05 Viikki (S) 92.725,06 Kalmari (M) 215.340,80 Maanika (M) 172.905,37 99 6.5.2. -Fertilization dosage according to Phosphorus extractions Using phosphorus extraction, fertilization dosage is: Table 59. Phosphorus extractions in maize, oilseed rape and hemp. Maize Oilseed Hemp Total P (g ha-1) 24.500 30.200 92.000 146.700 Phosphorus extraction has been calculated according to the extractions during three years of cropping, using the rotation of maize, oilseed rape and hemp, without considering losses by lixiviation and run-off. Table 60. Sludge and manure dosage according to phosphorus extraction (as dry matter). Dry matter Dosage kg ha-1 Forssa (S) 6.566,70 JKL (S) 7.240,87 Kouvula (S) 6.560,82 Vaasa (S) 6.985,71 Viikki (S) 4.876,99 Kalmari (M) 7.729,19 Maanika (M) 10.834,56 All those dosages are referred to dry matter, to calculate the real application dosage it must be divided by its dry matter content. 100 Table 61. Sludge and manure dosage according to phosphorus extraction (as fresh). Fresh Dosage kg ha-1 Forssa (S) 23.469,26 JKL (S) 24.298,22 Kouvula (S) 22.330,91 Vaasa (S) 23.680,37 Viikki (S) 16.100,99 Kalmari (M) 72.167,97 Maanika (M) 86.815,38 101 6.5.3. -Fertilization dosage according to Potassium extractions Using potassium extractions, fertilization dosage is: Table 62. Potassium extractions in maize, oilseed rape and hemp. Maize Oilseed Hemp Total K (g ha -1) 77.500 34.000 105.000 216.500 Potassium extraction has been calculated according to the extractions during three years of cropping, using the rotation of maize, oilseed rape and hemp, without considering losses by lixiviation and run-off. Table 63. Sludge and manure dosage according to potassium extraction (as dry matter). Dry matter Dosage kg ha-1 Forssa (S) 103.603,39 JKL (S) 105.123,11 Kouvula (S) 103.827,97 Vaassa (S) 104.386,15 Viikki (S) 104.254,95 Kalmari (M) 90.664,68 Maanika (M) 96.406,47 All those dosages are referred to dry matter, to calculate the real application dosage it must be divided by its dry matter content. Table 64. Sludge and manure dosage according to phosphorus extraction (as fresh). 102 Fresh Dosage kg ha-1 Forssa (S) 23.469,26 JKL (S) 24.298,22 Kouvula (S) 22.330,91 Vaasa (S) 23.680,37 Viikki (S) 16.100,99 Kalmari (M) 72.167,97 Maanika (M) 86.815,38 103 6.6. -Nutrient balance after fertilization and cropping 6.6.1. -Nutrient balance after Nitrogen based fertilization and cropping Table 65. Nutrient balance after nitrogen base dosage using sludge and manure. Balance Forssa (S) kg ha-1 JKL (S) kg ha-1 Kouvula (S) kg ha-1 Vaassa (S) kg ha-1 Viikki (S) kg ha-1 Kalmari (M) kg ha-1 Maanika (M) kg ha-1 P 389,49 217,76 368,99 297,72 502,38 254,44 233,59 C - 14.568 - 16.462 - 15.029 - 15.262 -15.701 - 13.037 - 10.294 N - - - - - - - As 0,07 0,04 0,07 0,06 0,06 0,09 0,14 Cd 0,01 0,00 0,01 0,01 0,01 0,01 0,01 Cr 0,47 0,30 0,46 0,38 0,41 0,62 0,91 Cu 6,24 4,61 6,00 5,48 5,62 0,57 1,09 K - 166,34 - 179,45 - 168,41 - 172,61 - 171,69 - 166,03 - 153,43 Ni 0,44 0,41 0,41 0,66 0,38 3,09 4,10 S - 122,31 - 122,83 -122,44 - 122,51 - 122,52 -123,62 - 123,45 Si 340,93 243,98 325,32 295,37 302,12 19,49 68,71 Zn 1,91 0,89 2,18 1,33 1,63 - 2,28 - 2,06 As we can observe in the balance, there is an important deficit of potassium when we based the dosage according to nitrogen extractions. In the other hand there are important accumulation of phosphorus (Table 65). 104 6.6.2. -Nutrient balance after Phosphorus based fertilization and cropping Table 66. Nutrient balance after phosphorus base dosage using sludge and manure. Balance Forssa (S) kg ha-1 JKL (S) kg ha-1 Kouvula (S) kg ha-1 Vaassa (S) kg ha-1 Viikki (S) kg ha-1 Kalmari (M) kg ha-1 Maanika (M) kg ha-1 P - - - - - - - C - 19.233 - 19.167 - 19.294 - 19.099 - 19.794 - 18.081 - 16.864 N - 462 - 380,60 - 455 - 426 - 493 - 404 - 391 As - 0,01 - 0,01 - 0,01 - 0,01 - 0,02 0,00 0,03 Cd - 0,00 0,00 0,00 0,00 - 0,00 0,00 0,00 Cr - 0,07 - 0,04 - 0,06 - 0,06 - 0,12 0,05 0,18 Cu 1,52 1,70 1,52 1,63 1,07 0,04 0,26 K - 202 - 201 - 202 - 202 - 206 - 198 - 192 Ni 0,08 0,14 0,08 0,18 0,05 1,10 1,55 S - 123 - 123 - 123 - 123 - 123 - 124 - 123 Si 60,73 71,44 60,49 67,49 33,61 - 21,29 - 1,01 Zn - 1,59 - 1,38 - 1,46 - 1,50 - 1,88 - 2,67 - 2,58 If we base the dosage in phosphorus extraction, there are important deficit in phosphorus and potassium (Table 66). 111 process. Regarding losses by leached, at pH lower than 7 (like this type of soil), losses by leaching decreases (Ahlberg et al., 2006). 7.1.5. -Manganese content In manganese we can observed that there are three statically different groups, one group of sewage sludge, sewage sludge from Jyvaskyla and manure. The first group range between 247-248 mg kg-1 and Jyvaskyla is in 250 mg kg-1. If we compare that result with other studies we can see that Fytili and Zabaniotou obteined 260 mg kg-1, quite similar to the result. Goi et al. obtained different results; they found that manganese in sewage sludge ranged from 10 to 100 mg kg-1, less than the half of the quantity founded in the results. Hernández et al obtained 169 mg kg-1, lower than the obtained values. Results from Erikson of 2001, 310 mg kg-1, are also in the same order of magnitude than the samples. In manure the average content of manganese was significantly higher than the content in sewage sludge. If we compare the results, 275-276 mg kg-1, to the average content of manganese found in manure in other study, 172 mg kg-1, we can see that the values found in those samples were higher than in the literature (Pomares and Canet, 2001). Again the difference can be cause by the different management of the feed and the microbes that can live in both places (Spain and Finland). In the soil that is studied there shouldn’t be problems of manganese, despite its low content 7,6 mg kg-1, with the low pH it will be quite soluble and available for the plant. An excessive application of manganese could lead to phytotoxicity problems, but to reach that is needed from 300 mg kg-1 in soy to near 2.000 mg kg-1 of dry matter in rice, levels that are difficult to reach using sludge or manure as a fertilizer source (Ahlberg et al., 2006). 112 7.1.6. -Sodium content Sodium content is significantly higher in manure than in sewage sludge, in the order of 100 mg kg-1 higher in sewage sludge. In manure, the study shows a content of 580mg/kg, similar to the 400-440 mg kg-1 founded in manure samples. To compare with sewage sludge is more difficult due to the lack of information about sodium content. Is relevant that the highest amount of sodium was founded in Forssa where the sludge is biologically digested. Excessive amounts of sodium can lead to pH increases and salinity problems, but with this kind of soil and the concentration in sludge and manure, there shouldn´t be any problems cause by sodium (Ahlberg et al., 2006). 7.1.7. -Copper content In most of the studies that analyze sewage sludge appears the quantity of copper. This interest for copper concentration in due to the fact that high concentrations of copper can lead to phytotoxicity and that’s why the European legislation has established a limit concentration for sludge in agricultural application which ranges from 1000-1750 mg kg-1 (European legislation) and a total amount of copper of 12kg/ha/year. There were significantly differences between sewage sludge concentrations and manure concentration, being around 270 and 39-48 mg kg-1respectively. Other studies like the one done by Wang et al in 2008 shows a content of 170 mg kg-1, Hernández et al obtained in 1990 152 mg kg-1, Cai et al obtained in 2007 396 mg kg-1 and Goi et al found a range of 12-100 mg kg-1. Erikson in 2001 also found similar values for copper, 390 mg kg-1. So the results are consistent with the values that appear in the literature. In addition, we can observe how those values of copper concentration are lower than the limit values established in the European legislation, so according to the copper limitation that sewage sludge can be apply in the field providing less than 12 kg ha-1 year-1, which means that we cannot apply more than 44 ton ha-1 year-1 of those sludge (in dry matter). This sludge samples showed the most limiting amount of sludge that can 113 be legally applied in the soil in the amount of sludge limited by its copper content (Tables 42 to 46). Copper can be quite soluble at low pH, like in the studied soil. That could lead to a higher solubilization of copper, as a result it can have higher phytotoxicity at the same concentration in an acid soil than in a basic soil (Ahlberg et al., 2006; Doelsch et al., 2006). 7.1.8. -Chromium content Chromium is other element that is restricted which content is restricted by the European legislation. The results obtained where much lower than some of the values observed in the literature, in the sewage sludge the values are around 31 mg kg-1and Fytili and Zabaniotou had observed 500 mg kg-1of Chromium, but there are other studies like the one done by Singh and Agrawal in 2007 where they found 35,5 mg kg-1which is much similar to the observed values. In adittion, Erikson found in 2001 33 mg kg-1, very close to the observed values. Manure as significantly higher concentration of chromium than in sewage sludge, with values of around 41 mg kg-1that are almost the half of the chromium content that is found in the literature, 24 mg kg-1. 7.1.9. -Zinc content Zinc is also restricted by European legislation and is quite usual to see zinc concentrations in chemical analysis of sludges. According to the literature the values can vary from 290 mg kg-1 (Wang et al., 2008), 780 mg kg-1 (Herández et al., 1990), 1213 mg kg-1, 20-400 mg kg-1 (Goi et al., 2006), 785 mg kg-1 (Singh and Agrawal., 2007) and 550 mg kg-1(Erikson, 2001). The results range from 200 to 220mg kg-1 in sewage sludge and are quite similar to the concentrations that appear in the literature, being more similar to the results given by Wang et al and Goi et al. 114 Concentrations in manure were much lower, 29 mg kg-1in both cases. This value is quite lower than the concentration that appears in the literature 133 mg kg-1. Again, this difference can be cause by the different environment and management of the farms. According to European legislation any sludge that has more than 2500-4000 mg kg-1 cannot be used for agricultural proposes. The total amount of zinc that can be legally applied on the field is 30kg ha-1 year-1. With those samples of sewage sludge the total amount of sludge that we have to apply to reach that level is 136 ton ha-1. 7.1.10. -Lead content Lead is other element of high risk of phytotoxicity and toxicity to humans and animals, that’s why the amount of this element in the sludge is restricted by the European legislation and is widely analyzed in the literature. According to the literature the concentrations of lead in sewage sludge are 255 mg kg-1 (Wang et al., 2009), 109 mg kg-1 (Hernámdez et al., 1990), 57 mg kg-1 (Cai et al., 2007) a60 mg kg-1 (Singh and Agrawal, 2007) and 33 mg kg-1 (Erikson, 2001). Results show significant differences between sewage sludge and manure. In sewage sludge the values ranges from 19 to 20 mg kg-1, and are quite smaller than the values obtained from the literature. Manure has slightly higher concentration of lead, 26 mg kg-1, than sewage sludge. Literature shows concentrations of 14 mg kg-1, almost the half of the obtained concentration. Looking at the European legislation we can see that that sludge meets with the limitation of lead concentration which is 750-1200 mg kg-1. The total amount of lead that can be legally apply on the field is 15kg/ha/year, so to reach these level would be necessary to apply more than 750 ton ha-1. 115 7.1.11. -Sulfur content Sulfur has been barely analyzed in the literature, one study where sulfur has been analyzed was done by Erikson in 2001, and he found out that sludge has 9.000 mg kg-1. There is just one study to compare, but the obtained result was much lower than this value. The results shows that manure has significantly less sulfur concentration (30-32 mg kg-1) than the sewage sludge concentration (80-84 mg kg-1). Due to the humidity of the Finnish climate, there could be important losses of sulfur, but they will be less important than nitrogen losses, because of its lower solubility. In addition, water used for irrigation can have enough sulfur to cover crop needs, as an example, the water used by Casado-Vela in 2007 to irrigate sweet pepper contained 130 mg L-1, higher amount than which is present in manure or the sludge. 7.1.12. -Silicon content There is lack of information in the literature about silicon content in sludge and manure, it appears as a secondary data in the study of Fytili and Zabaniotou of 2008, where they mention a silicon content of 100.000-200.000 mg kg-1, it also appear in the study done by Erikson in 2001 where he measured a value of 45.000 mg kg-1. The results shows values much lower than those concentrations, in sludge they are around 16.000 mg kg-1 and in manure in the order of 3.000-4.000 mg kg-1. Moreover, silicon isn’t a key element in crop fertilization. 7.1.13. -Aluminum content Aluminum hasn’t been deeply analyzed in literature, as the case of silicon is not considered as a key element in crop fertilization. One example where aluminum has been analyzed is the study done by Erikson in 2001, and the measured concentration of 116 aluminum was 40.000 mg kg-1. The results are ten times lower, in the order oF 4.000 mg kg-1. 7.1.14. -Iron content Most of soil analysis shows values of 1.5-6 mg kg-1 of iron, but the result showed 150 mg kg-1 of iron, extremely higher than most of the soils that appear in literature. Looking at the iron concentration in manure, the result is even more inordinately higher, with concentrations of 500 mg kg-1, but the manure analysis done by Pomares and Cannet showed contents of 4100 mg kg-1 so much higher than the results. In sludge the literature is quite confusing, some studies like Casado-Vela shows values of 5 mg kg-1, but others like Fytili and Zabaniotou shows values of 2.500 mg kg-1. Looking at those values, the result of a concentration of around 17.000 mg kg-1 is closer to the result obtained by Fytili and Zabaniotou. Comparing the results with the data obtained from Erikson in 2001, we can observe that the obtained results are quite lower than the concentration in his study, 49.000 mg kg-1. Probably there has been contamination or errors in the measurement of the iron, otherwise sludge application in the soil should lead to considerable phytotoxicity problems, and the field trials doesn’t show that. Iron increases its solubility by the decrease of pH. In the type of soil that is studied, iron is quite soluble, and there could be excessive iron available for the plant. Although there could be high precipitation rate in the form of iron phosphates, that can allow to reduce the possible negative effects that high iron content could cause. 7.1.15. -Arsenic content Arsenic can be toxic in high concentration, but it not common to found high amounts of arsenic in the soil. Manure had higher values than sludge, but still they were below the 10 mg kg-1 that was reported by Fitily and Zabiniotou in 2008 in sewage sludge. In contrast the obtained values were practically the same as the obtained by Erikson in 117 2001. So arsenic content shouldn´t be considered as a limiting element for sludge application. 7.1.16. -Cadmium content High concentration of cadmium can be harmful for the plants and then for the animals, that’s why is included in the European legislation and included in many legislation of countries and region that regulates sludge application. European Union established a limit amount of 20 mg kg-1, in Spain is also 20 mg kg-1 and Finland is lower, 3 mg kg1. The studied sludge had between 0,40 and 0,46 mg kg-1of cadmium, bellow the limit, so it can be legally used. The soil had 0,11 mg kg-1 of cadmium also below the limit of 0,5 mg kg-1 that is established in the exigent Finnish legislation, in Spain the limit is 1 mg kg-1 and in Europe 3 mg kg-1. Literature shows more or less values similar to the obtained in the analysis. Pomares and Canet found 1 mg kg-1in manure. Goi et al found that cadmium levels were below 2 mg kg-1 in all the samples that they analyzed. Casado-Vela measured 0,15 mg kg-1. So all the references shows similar values. Erikson found 1,5 mg kg-1, a bit higher than the obtained result. 7.1.17. -Calcium content Comparing the data with the literature we can see that sludge results are very near to the results obtained by Casado-Vela et al in 2007, in the order of 38.500 mg kg-1. In the other hand, De Saavedra in 2000 found 76.000 mg kg-1 of calcium, but this is not measured in elemental calcium, is measured in its fertility unit (CaO) and if we extrapolate this result to elemental calcium the results shows 54300 mg kg-1, quite higher to the results, but still near. Results in manure were less close to the values found in literature, 37.400 mg kg-1 of CaO (Pomares and Canet, 2001): In a study done by ICP analysis (Erikson, 2001) the result was 28.000 mg kg-1, somehow close to the results. In this case is also measured in fertility units, but if we extrapolate it to 118 elemental calcium, the result is 26.700 mg kg-1, much higher than the 3.200 mg kg-1 found in manure. Despite the low pH, calcium content in the soil is quite high, with more than 9.000 mg kg-1. Usually is soils with low pH, as this one, there is low calcium concentration and is necessary to apply calcium amendments, in many cases is done using manure which in this case has around 3.000 mg kg-1, but this results shows that could be more efficient sludge, due to its high content in calcium that is in the order of 38.200-38.500 mg kg-1. 7.1.18. -Magnesium content Sludge and manure showed similar values for magnesium content, in the order of 3.400 mg kg-1. Looking at literature, we can see similar values, like the 2650 mg kg-1 found by Casado-Vela in 2007, the result is almost the same as the result obtained by Erikson in 2001. In contrast, literature show higher values for manure 10.800 mg kg-1 (Pomares and Canet, 2001). The soil showed a normal content of magnesium, 109,17 mg kg-1. 7.1.19. -Nickel content Nickel content was quite close to the limit established in the Spanish legislation of 30 mg kg-1, in the other hand was farther to the Finnish limitation of 100 mg kg-1. Manure clearly exceeded both limits with a concentration of 147 mg kg-1. This values is too high, especially if we compare it with the measured obtained by Pomares and Canet in 2001 of 20 mg kg-1. There could be cause by the different management of the farms, but considering that the obtained value is extremely high, is possible that there has been some kind of sample contamination. Comparing the results in sludge with literature, we can see that they are similar to the results obtained by Erikson in 2001 and Goi et al in 2005. The others studies shows higher concentrations. 119 7.2. -Legal requirements The soil was fulfills the legal requirements in all the studied countries. Cadmium content in the soil showed a value near to the exigent Finnish legislation, but was below the limit. The rest of the limited elements had concentrations that were far from the limit. All the sludge samples can be legally used for agricultural proposes according to the European legislation (86/278/EEC), Spanish legislation (Minesterio de Agricultura, Pesca y Alimentación, 1310/1990) and Finnish legislation (Ministry of Agriculture and Forestry, 282/1994). In cadmium there would be needed three times higher concentration to be over the limit. Regarding chromium, the difference is even higher, in the order of ten times higher. For copper, like cadmium, there would be needed three times more copper than which is established in the most exigent legislation (Finnish). In any of the samples was detected mercury, so there aren’t any problems with mercury. Nickel has the lowest value in the Finnish legislation, but still there would be needed 5 times more nickel than which is present to cannot be legally used. In the case of lead, as in most of the heavy metals, the most limiting legislation is the Finnish legislation, but to don’t fulfill the legal requirements there would be needed five times more lead than the measured concentration. Surprisingly the Spanish legislation was the most exigent according to zinc concentration, but it was more than the double amount of zinc that which is present in the sample. In manure there are problems in nickel concentration, which is slightly higher than the established in the Spanish and the Finnish legislation, but it was lower than the established in the European Directive. Despite the fact that being over the limits in the two studied countries, there wouldn´t be any legal problem to use this manure as fertilizer, due to the fact that this product is not included in those legislation. The rest of the elements were far from the limits, and if they would have been over the limits, there wouldn’t be any legal problem as it was told before. In sludge, European and Spanish legislation have more or less the same limit amount of sludge that can be applied per year. In the studied sludge, for those legislation the most limiting was copper, with a maximum of 44.000 kg ha-1. However, Finnish is much 120 more restrictive, especially in the case of copper, were the maximum amount of sludge that can be legally applied per year is 2.200 kg ha-1. Manure, as we have said before, is not regulated by this legislation, but using the same restrictions as sludge we can fix a limit for maximum dosage according to heavy metal accumulation. This manure didn´t fulfill nickel requirements, and consequently the most limiting element was nickel with a value of approximately 20.000 kg ha-1 in the European Union and Spain, and around 680 kg ha-1 in Finland. 7.3. -Fertilization dosage 7.3.1. -Nitrogen based dosage If we make the dosage according to nitrogen extraction there will be needed 637 kg ha-1 of Nitrogen to compensate the nitrogen exportations during crop harvest. For most of the sludge samples it would be required the same amount, in the order of 21.000-24.000 kg ha-1. If we use sludge from Jyvaskyla there would be needed less amount of sludge due to its higher amount of nitrogen. In the other hand, using manure from Maanika there would be needed 28.000 kg ha-1. According to the legislation that we have previously analyzed, there is a maximum amount of sludge that can be applied on the soil according to its heavy metal content. So in our case, the soil is located in Finland, so the maximum amount of sludge than can be legally applied per year is 2.200 kg ha-1. This value is much lower than the amount needed, but this legal value is consider as an average amount of sludge applied in a period of ten years (Finnish Decree), so for example in this case we can make one fertilization per each three years, and the maximum amount of sludge that could be applied will be 6.600 kg ha-1, or in the case that we left the field without cropping one year, the fertilization will be one time per each four year, and as a consequence the maximum amount of sludge that could be applied will be 8.800 kg ha-1. We can observe that even in the case of keeping one year without cropping, the maximum amount of sludge that can be legally applied is less than the half that is needed to fulfill nitrogen requirements. 127 128 9. 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